Satellite radio wave receiving device, electronic timepiece,  positioning control method, and non-transitory computer-readable storage medium

ABSTRACT

A satellite radio wave receiving device including: one or more processors configured to: cause a receiver to start a receiving operation of receiving radio waves from positioning satellites; perform a current position calculation to calculate a current position based on the radio waves received; calculate a positioning accuracy of the current position; decide whether or not to adopt the current position based on a number of positioning satellites from which the receiver has received radio waves and the positioning accuracy; in response to deciding to adopt the current position, cause the receiver to stop the receiving operation; and in response to deciding to not adopt the current position, cause the receiver to continue the receiving operation of receiving radio waves from the positioning satellites and repeat performance of the current position calculation to calculate current positions based on the radio waves received during the continued receiving operation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims priority to prior JapanesePatent Application No. 2018-040629, filed on Mar. 7, 2018, the entirecontent of Japanese Patent Application No. 2018-040629 is incorporatedherein by reference.

BACKGROUND

The technical field relates to a satellite radio wave receiving device,an electronic timepiece, and a positioning control method.

Conventionally, a positioning device identifies the current position byreceiving radio waves from positioning satellites and performingcalculation for positioning. In order to obtain a current position, itis necessary to receive radio waves from at least three or foursatellites. As the number of received radio signals (the number ofpositioning satellites) used for positioning calculation increases, thepositioning accuracy is generally improved. On the other hand, forreceiving radio waves from many positioning satellites, a load for radiowave capturing operation from the positioning satellites and the timerequired to capture radio waves from the large number of positioningsatellites increase, so that the power consumption increases.

For example, a Japanese patent document JP2014-66550A discloses atechnique in which, if radio waves from a predetermined number ofpositioning satellites are captured during continuous positioningoperation, the radio wave capturing operation from the furtherpositioning satellite is not performed and positioning calculation isperformed by the radio signal from the captured positioning satellites,and if the number of the captured radio waves becomes less than thepredetermined number, the capturing operation is restarted.

However, depending on the position of the captured positioningsatellites and their distribution, sufficient positioning accuracy maynot be obtained in some cases, using only the number of capturedpositioning satellites. That is, conventionally, appropriate obtainingaccuracy in the current position and suppression of power consumptionhave not been achieved simultaneously.

SUMMARY

A satellite radio wave receiving device, an electronic timepiece, amethod, and a computer-readable storage medium storing instructions forcontrolling a positioning operation are disclosed.

In an embodiment, there is provided a satellite radio wave receivingdevice comprising: one or more processors configured to: cause areceiver to start a receiving operation of receiving radio waves frompositioning satellites; perform a current position calculation tocalculate a current position based on the radio waves received by thereceiver; calculate a positioning accuracy of the current position;decide whether or not to adopt the current position based on a number ofpositioning satellites from which the receiver has received radio wavesand the positioning accuracy of the current position; in response todeciding to adopt the current position, cause the receiver to stop thereceiving operation; and in response to deciding to not adopt thecurrent position, cause the receiver to continue the receiving operationof receiving radio waves from the positioning satellites and repeatperformance of the current position calculation to calculate currentpositions based on the radio waves received during the continuedreceiving operation.

In another embodiment, there is provided a satellite radio wavereceiving device comprising: means for causing a receiver to start areceiving operation of receiving radio waves from positioningsatellites; means for performing a current position calculation tocalculate a current position based on the radio waves received by thereceiver; means for calculating a position accuracy of the currentposition; means for deciding whether or not to adopt the currentposition based on a number of positioning satellites from which thereceiver has received radio waves and the positioning accuracy of thecurrent position; and means for, in response to deciding to adopt thecurrent position, causing the receiver to stop the receiving operation;and means for, in response to deciding to not adopt the currentposition, causing the receiver to continue the receiving operation ofreceiving radio waves from the positioning satellites and repeatingperformance of the current position calculation to calculate currentpositions based on the radio waves received during the continuedreceiving operation.

In another embodiment, there is provided a positioning control methodperformed by a satellite radio wave receiving device including areceiver, the method comprising: causing the receiver to start areceiving operation of receiving radio waves from positioningsatellites; performing a current position calculation to calculate acurrent position based on the radio waves received by the receiver;calculating a positioning accuracy of the current position; decidingwhether or not to adopt the current position based on a number ofpositioning satellites from which the receiver has received radio wavesand the positioning accuracy of the current position; in response todeciding to adopt the current position, causing the receiver to stop thereceiver operation; and in response to deciding to not adopt the currentposition, causing the receiver to continue the receiving operation ofreceiving radio waves from the positioning satellites and repeatingcalculation of the current position calculation to calculate currentpositions based on the radio waves received during the continuedreceiving operation.

In another embodiment, there is provided a non-transitorycomputer-readable storage medium storing instructions that cause one ormore computers to at least perform: causing a receiver to start areceiving operation of receiving radio waves from positioningsatellites; performing a current position calculation to calculate acurrent position based on the radio waves received by the receiver;calculating a positioning accuracy of the current position; decidingwhether or not to adopt the current position based on a number ofpositioning satellites from which the receiver has received radio wavesand the positioning accuracy of the current position; in response todeciding to adopt the current position, causing the receiver to stop thereceiving operation; and in response to deciding to not adopt thecurrent position, causing the receiver to continue the receivingoperation of receiving radio waves from the positioning satellites andrepeating performance of the current position calculation to calculatecurrent positions based on the radio waves received during the continuedreceiving operation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a functional configuration of anelectronic timepiece according to an embodiment.

FIG. 2 illustrates a method of calculating accuracy.

FIG. 3 illustrates a relation between a signal-to-noise ratio (SNR) ofradio waves received from a positioning satellite and a ranging accuracyfor the positioning satellite from which radio waves are received at theSNR.

FIG. 4 illustrates a control procedure of a positioning control process.

FIG. 5 illustrates a control procedure of an intermittent positionobtaining process.

FIG. 6 illustrates a modification example of an intermittent positionobtaining process.

DETAILED DESCRIPTION

An embodiment will now be described with reference to the drawings.

FIG. 1 is a block diagram illustrating a functional configuration of anelectronic timepiece 1 according to an embodiment.

An electronic timepiece 1 includes a microcomputer 40, a satellite radiowave receiving unit 50, an antenna Al, an operation receiver 61, adisplay 62, a read only memory (ROM) 63, and a power supply 70.

The microcomputer 40 performs various kinds of operation, such ascontrol of the electronic timepiece 1, storage in memory, and countingof date and time. The microcomputer 40 includes a host processor 41, anoscillating circuit 45, a frequency dividing circuit 46, and a timingcircuit 47 (a clock circuit).

The host processor 41 administers the overall operation of theelectronic timepiece 1. The host processor 41 includes a centralprocessing unit (CPU) 411 and a random access memory (RAM) 412.

The CPU 411 performs various calculations to control a normal display ofdate and time and operation relevant to the various functions of theelectronic timepiece 1, such as alarm notification. The CPU 411 alsoobtains the results of the positioning operation and the date and timeobtaining operation performed by the satellite radio wave receiving unit50 and controls display and notification based on the obtained results.

The RAM 412 provides the CPU 411 with a working memory and storestemporary data. The temporary data includes information on time zonesettings and local time settings (including daylight-saving time). Thetime zone settings are used to display the current date and time (localtime) at a set position, such as the current position, in a region inthe world. These local time settings may be updated in accordance withthe current position information adopted through the positioningoperation. The RAM 412 may be external to the microcomputer 40. The RAM412 may also include a rewritable non-volatile memory in addition toDRAM.

The oscillating circuit 45 generates and outputs a signal with apredetermined frequency of, for example, 32.768 kHz (clock signal). Acrystal oscillator, for example, is used to generate clock signals. Thecrystal oscillator may be external to the microcomputer 40. Thefrequency of the clock signals output from the oscillating circuit 45may contain errors within an allowable range for the electronictimepiece 1.

The frequency dividing circuit 46 frequency-divides the clock signalsinput from the oscillating circuit 45 into frequency-division signalswith a predetermined frequency division ratio, and outputs thefrequency-division signals. The frequency dividing circuit 46 may outputfrequency-division signals of multiple frequencies. The frequencydivision ratio may be changed by the CPU 411.

The timing circuit 47 counts signals with a predetermined frequencyinput from the frequency dividing circuit 46, which may be identical tothat of the clock signals, to count and retain the current date andtime. The accuracy of the date and time counted by the timing circuit 47depends on the accuracy of the clock signals from the oscillatingcircuit 45. The date and time counted by the timing circuit 47 maydeviate from an accurate date and time. The CPU 411 can modify thecounted date and time based on the current date and time obtained by thesatellite radio wave receiving unit 50.

The satellite radio wave receiving unit 50 is a satellite radio wavereceiving device according to the present embodiment, and can receiveradio waves transmitted from a positioning satellite in a globalnavigation satellite system (GLASS), such as Global Positioning System(GPS) of the U.S.A., and a system for compensation thereof. Thesatellite radio wave receiving unit 50 processes the received radiowaves to obtain and/or adopt information on the current date and timeand the current position. In response to a request of the host processor41 (CPU 411), the satellite radio wave receiving unit 50 outputsrequested information in a predetermined format to the host processor41. The satellite radio wave receiving unit 50 includes a receiver 51, amodule processor 52, and a memory 53.

The receiver 51 receives radio waves transmitted from a targetpositioning satellite. As the receiving operation, the receiver 51receives and detects radio waves including signals (a navigationmessage) transmitted from the positioning satellite, and performs theacquiring process for identifying the positioning satellite and thephase of the a navigation message. The receiver 51 tracks the radiowaves transmitted from the positioning satellite based on theidentification information on the acquired positioning satellite and thephase, and continuously demodulate and receive the signals.

The module processor 52 includes a CPU and a RAM and controls thevarious kinds of operation of the satellite radio wave receiving unit50. In response to an instruction of the host processor 41, the moduleprocessor 52 causes the receiver 51 to receive radio waves from apositioning satellite at an appropriate timing and period. The moduleprocessor 52 functions as an activation controller 521, a calculator522, an adoption determiner 523, and a stop controller 524. The moduleprocessor 52 obtains necessary information from the radio waves receivedat the receiver 51 to perform various calculations as needed, andobtains and/or adopts the current date and time and/or the currentposition. The module processor 52 may be provided with a dedicatedhardware circuit for various calculations. The positioning result may beoutput in a common format such as NMEA-0183, or in a format specific tothe electronic timepiece 1. The data output by the hardware circuit in apredetermined format may be processed as needed and output by the CPU.The RAM is provided on a control chip (substrate) of the moduleprocessor 52. Alternatively, the RAM may be externally mounted on thecontrol chip. When the current date and time and the current positionare obtained and adopted, the module processor 52 can calculate valuesregarding a moving speed and acceleration of the current position, anSNR (signal-to-noise ratio defined the same as a C/N ratio here) ofradio waves from each positioning satellite, a direction (elevationangle, azimuth angle) of each positioning satellite from the currentposition, dilution of precision (DOP), and positioning accuracydescribed later.

The memory 53 stores receipt controlling information 531, such asvarious parameters and received information, and control programsexecuted by the module processor 52 in the satellite radio wavereceiving unit 50. Examples of the parameters include format data fornavigation messages from each positioning satellite. The receivedinformation includes, for example, predicted orbit information (almanac)and precise orbit information (ephemeris), which are obtained from eachpositioning satellite. The memory 53 is a non-volatile memory and may beexternal to a control chip (a substrate) of the module processor 52.

The operation receiver 61 receives external input operation, such asuser operation. The operation receiver 61 includes a push-button switchand a winding crown. In response to pressing operation of thepush-button switch or a pulling-out, rotating, or pushing-back operationof the winding crown, the operation receiver 61 outputs a correspondingoperational signal to the host processor 41 (the CPU 411).Alternatively, the operation receiver 61 may include a touch sensorprovided on the display screen 621 of the display 62.

The display 62 shows various pieces of information in accordance withthe control of the host processor 41. The display 62 includes a displaydriver 622 and a screen 621. The screen 621 displays digital informationon a liquid crystal display (LCD) of a segment, dot-matrix orcombination type. Alternatively, the display 62 may be configured toshow information with needles and a stepping motor that rotates theneedles, instead of the digital display on the display screen 621. Inresponse to a control signal from the CPU 411, the display driver 622outputs a drive signal on the display screen 621 to show information onthe display screen 621. The information appearing on the display 62includes the date and time information (in particular, the current dateand time) according to the date and time counted by the timing circuit47, and other functions of the electronic timepiece 1 such as set timeinformation on alarm notification. Information on the current positionadopted through positioning operation and local time settings can alsobe displayed.

The ROM 63 stores programs 631 and initial setting data. The programs631 are for the host processor 41 and the module processor 52 to performcontrol operation. The ROM 63 may store a non-volatile memory, such as arewritable and updatable flash memory, in addition to or in place of amask ROM. The ROM 63 is read- and write-accessible by the host processor41 and the module processor 52 and detachable from a mount portion, suchas a slot.

The programs 631 include control programs for obtaining and adopting thecurrent time and date and positioning operation. The ROM 63 containsranging accuracy/SNR conversion data 632 that indicates thecorrespondence relation between the received strength of radio wavesreceived by the satellite radio wave receiving unit 50 and the rangingaccuracy corresponding to the received strength of the radio waves,i.e., the expected deviation between the measured current position andthe actual position of the electronic timepiece 1 (the satellite radiowave receiving device). The ranging accuracy/SNR conversion data 632 maybe in the form of a table of the correspondence between SNRs and rangingaccuracies, or a formula or approximation formula, for calculating theranging accuracy from a SNR. The ranging accuracy/SNR conversion data632 may be stored in the memory 53 of the satellite radio wave receivingunit 50.

The power supply 70 supplies power from a battery 71 to various units ofthe electronic timepiece 1, such as microcomputer 40 and the satelliteradio wave receiving unit 50, at a predetermined drive voltage. Thesupply or non-supply of power to the satellite radio wave receiving unit50 can be controlled separately from power supply to the microcomputer40 under the control of the host processor 41. The battery 71 is areplaceable dry-cell battery or a rechargeable battery. The power supply70 may include solar panels and an electricity charging unit (powerstorage) as the battery 71.

Next, the positioning operation of the electronic timepiece 1 accordingto this embodiment will now be described.

The satellite radio wave receiving unit 50 of the electronic timepiece 1receives radio waves from a plurality of (i.e., three or more)positioning satellites to obtain navigation messages. The electronictimepiece 1 performs positioning calculations based on the receivednavigation messages and the timing to receive the navigation messages.In the positioning calculations, the electronic timepiece 1 calculatesthe accuracy of the positioning result (positioning accuracy).

A navigation message received from each of four or more positioningsatellites (if there are three positioning satellites, the altitude ofthe current position is set as a fixed value) contains an ephemeris. Inthe positioning calculations, the current position of each satellitebased on the ephemeris and a difference in the timing to receive thenavigation message from each positioning satellite (pseudo range) areused to calculate four (three if the altitude is fixed) unknowns, i.e.,three (two if the altitude is fixed) components of the current positionof electronic timepiece 1 and a component of the current time and date.This calculation is performed by an iterative calculation (successiveapproximation), for example, the Newton-Raphson method (Newton'smethod). The iterative calculation involves a numerical convergence of apredetermined initial value to an unknown value. At this time, a valuecorresponding to the error range of the current position can becalculated as the positioning accuracy, considering the positionalrelationship of the multiple positioning satellites from which the radiowaves have been received and a receiving state of the received radiowaves.

FIG. 2 illustrates a method of calculating the accuracy of theelectronic timepiece 1 according to this embodiment.

For a positioning satellite from which radio waves can be received, itsrelative direction to the current position is determined with anelevation angle φ and an azimuth angle λ. The elevation angle φ is anangle between the line connecting the current position and thepositioning satellite and a horizontal plane E; a direction x₃ isperpendicular to the horizontal plane E. The azimuth angle λ is an anglebetween the component on the horizontal plane E of the line connectingthe current position and the positioning satellite and the north poledirection N; the north pole direction N is defined by the direction x₁and the direction perpendicular to the direction x₁ on the horizontalplane E is defined by a direction x₂. When multiple positioningsatellites from which radio waves are received are distributedappropriately, more accurate three components of the current positionand a more accurate time component can be obtained. If the multiplepositioning satellites are distributed unevenly with respect to thecurrent position, the obtained accuracy is low. Depending on thedirection of uneven distribution, for example, the horizontal positionaccuracy may be good but the vertical position (altitude) accuracy maynot very good, for example.

The dilution of precision (DOP) used as an index of positioning accuracyis represented by D=A^(T)·A on a matrix A (x) of n rows and 4 columnsthat consists of three directional components (x_(ij), j=1 to 3)relative to the current position of each positioning satellite s_(i)(i=1 to n, n represents the number of positioning satellites used forpositioning) and a time component (x_(i4); here, x_(i4)=1), i.e., thediagonal component of the inverse matrix D⁻¹=U of the matrix D of fourrows and four columns having j and k components which are expressed withD_(jk)=Σ_((i=1−n)) (x_(ij)·x_(ik)). This indicates that DOP solelydepends on the position of each positioning satellite s_(i). The threedirectional components of the i-th positioning satellite having a vectorlength of 1 can be calculated with (x_(i1), x_(i2), x_(i3))=(cosλ_(i)·cos φ_(i), sin λ_(i)·cos ϕ_(i), sin ϕ_(i)). As a result, HDOP, aDOP regarding accuracy in horizontal direction, is expressed by(|u₁₁|+|u₂₂|)^(1/2) using diagonal components u_(ii) of the matrix U;VDOP, a DOP regarding accuracy in vertical direction, is expressed by(|u₃₃|)^(1/2); PDOP, a DOP regarding accuracy in positional coordinate,is expressed by (Σ_((i=1 to 3))|u_(ii)|)^(1/2). These DOP values areeach approximately 1 under the best conditions; a greater value indicatea lower accuracy.

In the electronic timepiece 1 according to this embodiment, an accuracyindex value obtained by weighting the arrangement of each positioningsatellite (the relative direction from the current position) with theranging accuracy corresponding to the received radio wave intensity(here, SNR) from the positioning satellite is calculated.

FIG. 3 illustrates a relation between a SNR of radio waves received froma positioning satellite and a ranging accuracy for the positioningsatellite from which radio waves are received at the SNR.

As an SNR [dBHz] reduces, the accuracy for determining a pseudo range (aranging accuracy e_(i) [km]) also deteriorates (the value increases),i.e., the maximum deviation expected at a position obtained throughpositioning increases. As shown by the solid line a in FIG. 3, theranging accuracy e_(i) improves (its value decreases) in accordance withan exponential function, as the SNR increases. This relation is storedas the ranging accuracy/SNR conversion data 632 in the ROM 63 beforeshipment of the product in the form of table data obtained based onmeasurements (or examination) or a calculating formula. In the casewhere the ranging accuracy/SNR conversion data 632 is in the form oftable data, the ranging accuracy e_(i) corresponding to the intermediatevalue among the SNR values in the table maybe calculated throughinterpolation. In the case where the ranging accuracy/SNR conversiondata 632 in the form of calculating formula, the calculating formula maybe an approximation formula provided that required accuracy is retained.The calculating formula may be simply expressed by a combination ofseveral straight lines, for example, as shown by the broken line b inFIG. 3.

As described above, radio waves are received from a plurality ofpositioning satellites and used to perform positioning operation. Acombination of SNRs or ranging accuracies e_(i) of positioningsatellites causes a variation in the maximum deviation that may beincluded in the final positioning result. Here, the first error range iscalculated as follows: Each element (x_(ij)·x_(ik)) of each componentD_(jk)=Σ_((i=1 to n)) (x_(ij)·x_(ik)) of the matrix D is weighted withthe ranging accuracy e_(i) corresponding to the SNR for each positioningsatellite s_(i), i.e., with e_(i) ⁻². Using the weighting matrix W of nrows and n columns having diagonal components w_(ii) set to e_(i) ⁻²(all non-diagonal components are set to “0”), the positioning accuracyΔx weighted with a received strength by D⁻¹=U, the inverse matrix of thematrix D=A^(T)·W·A (each component D_(jk)=Σ_((i=1 to n))(x_(ij)·w_(ii)·x_(ik))) is calculated. As described above, the DOPvalues under the best conditions are approximately 1. Therefore, thepositioning accuracy Δx (such as Δh corresponding to HDOP and Δzcorresponding to VDOP) is in the same order as that of the square rootof the square of a ranging accuracy e_(i), i.e., the same order as thatof the ranging accuracy e_(i). Alternatively, the positioning accuracyΔx may be suitably multiplied by a predetermined factor. In this way, anaccuracy index related to the positioning accuracy can be obtained inconsideration of not only the arrangement of the positioning satellitesbut also the radio wave reception state.

Next, the intermittent positioning operation of the electronic timepiece1 (satellite radio wave receiving device) according to this embodimentwill now be described.

In the electronic timepiece 1, one positioning result is adopted atevery predetermined time period (here, for example, one minute). Thereceiver 51 starts receiving operation every time the predeterminedperiod (one minute) elapses, and the positioning calculation isperformed every second. The satellite radio wave receiving unit 50determines whether or not the number of positioning satellites fromwhich the radio waves are received and the positioning accuracy value ofthe calculated current position satisfy the predetermined accuracycondition. When the accuracy condition is satisfied, it is decided toadopt the current position (positioning result), and the currentposition is adopted. Thereafter, the positioning calculation isterminated and the receiving operation by the receiver 51 is alsostopped. If the accuracy condition is not satisfied, the receivingoperation and the positioning operation are continuously repeated. If apositioning result satisfying the accuracy condition cannot be adoptedwithin the receiving time limit (upper limit) which is less than apredetermined period, here, for example, 30 seconds or less, the bestresult (the one with the highest positioning accuracy) obtained withinthat 30 seconds is adopted.

FIG. 4 is a flowchart illustrating a control procedure performed by themodule processor 52 for controlling the positioning process in theelectronic timepiece 1 according to this embodiment.

This positioning control process is started when the operation receiver61 receives a predetermined input operation. Alternatively, it may beactivated automatically when the electronic timepiece 1 is activated.

At the start of the positioning control process, the module processor 52activates the receiver 51 to start receiving radio waves frompositioning satellites (Step S101). The module processor 52 causes thereceiver 51 to perform an acquiring operation of radio waves frompositioning satellites and to start tracking operation as soon as theradio waves are acquired (Step S102). When radio waves of the requirednumber of positioning satellites are obtained, the module processor 52obtains the initial position by performing positioning calculation (stepS103).

The module processor 52 determines whether a termination instruction onpositioning operation has been obtained (step S104). The terminationinstruction on positioning operation is sent from the host processor 41if the operation receiver 61 received a predetermined input operation,or if the operation proceeds to a power save mode in which thepositioning operation is stopped due to insufficient power supplied fromthe power supply 70, for example. If it is determined that thetermination instruction has been obtained (“YES” at step S104), themodule processor 52 performs processing for terminating positioningoperation (step S108), and terminates the positioning control process.

If it is determined that the termination instruction on positioningoperation has not been obtained (“NO” in step S104), the moduleprocessor 52 determines whether or not it is the processing timingrelated to the intermittent position obtaining process (step S105). Thisprocessing timing may be, for example, once per second, and may besynchronized with the timing of the exact second of the date and timecounted by the timing circuit 47, or may be a timing of one secondperiod from an arbitrary timing. If it is determined that it is not theprocessing timing (“NO” in step S105), the module processor 52 repeatsthe process of step S105.

If it is determined that it is the processing timing (“YES” in stepS105), the module processor 52 invokes and executes the intermittentposition obtaining process (step S106). After termination of theintermittent position obtaining process, the module processor 52 outputsoutput setting data at an appropriate timing (step S107). The outputdata is output to a positioning history information 532 of the storageunit 53 and the host processor 41. The output to the host processor 41may be performed based on a request from the host processor 41. Then,the process of the module processor 52 returns to step S104.

FIG. 5 is a flowchart illustrating a control procedure performed by themodule processor 52 for the intermittent position obtaining processcalled in the positioning control process.

When the intermittent position obtaining process is called, the moduleprocessor 52 reads the cycle counter value Nm from the RAM (step S151).This cycle counter value Nm is for counting one minute period related tothe frequency of executing intermittent positioning. The moduleprocessor 52 adds “1” to the cycle counter value Nm (step S152). Themodule processor 52 determines whether or not the receiving operation ofthe receiver 51 is in progress (step S153).

If it is determined that the receiving operation is not in progress(“NO” in step S153), the module processor 52 determines whether or notthe cycle counter value Nm is “60” (step S154). If it is determined thatthe value is not “60” (“NO” in step S154), the module processor 52terminates the intermittent position obtaining process and returns theprocess to the positioning control process.

When it is determined that the cycle counter value Nm is “60” (“YES” instep S154), the module processor 52 activates the receiver 51 and startsreceiving operation and positioning calculation process (step S155;activation controller, activation control step). The module processor 52initializes the cycle counter value Nm to “0” (step S156). The moduleprocessor 52 initializes the accuracy index minimum value Δhm and erasesthe stored optimum result (step S157). The initial value of the accuracyindex minimum value Δhm is a fixed value recognized as an initial valuein the process, a second reference value H2 as a positioning accuracyindex Δh, and the like. The second reference value H2 is, for example,100 (meters).

The module processor 52 performs positioning calculations based on thecontents received by the receiver 51 and stores the positioning result.The stored positioning result may be overwritten and updated each time.Further, the module processor 52 calculates and stores the abovepositioning accuracy value Δx (=(Δh, Δz)) as the accuracy index value(step S 158; calculator, calculation step). Then, the module processor52 terminates the intermittent position obtaining process and returnsthe process to the positioning controller.

If it is determined that receiving operation of the receiver 51 is inprogress (“YES” in step S153) in the determination processing in stepS153, the module processor 52 determines whether or not the cyclecounter value Nm is a value corresponding to the receiving time limit(“30” here) (step S161). If it is determined that the cycle countervalue Nm is “30” (“YES” in step S161), the process proceeds to stepS171. If it is determined that the cycle counter value Nm is not “30”(“NO” in step S161), the module processor 52 reads the storedpositioning accuracy index Δh regarding the horizontal direction storedin the RAM (step S162).

The module processor 52 determines whether or not the positioningaccuracy index Δh is equal to or less than the second reference value H2and equal to or less than the stored accuracy index minimum value Δhm(whether or not the positioning accuracy satisfies a first criterion)(step S163). If the initial value of the accuracy index minimum valueΔhm is the second reference value H2 as described above, since theaccuracy index minimum value Δhm is necessarily less than or equal tothe second reference value H2, comparison with the second referencevalue H2 is not necessary. If it is determined that at least one of themis not satisfied (“NO” in step S163), the process of the moduleprocessor 52 proceeds to step S158.

If it is determined that the positioning accuracy index Δh is equal toor less than the second reference value H2 and equal to or less than theaccuracy index minimum value Δhm (“YES” in step S163), the moduleprocessor 52 sets the positioning accuracy index Δh as the accuracyindex minimum value Δhm. The module processor 52 causes the RAM toseparately update the stored positioning result as an optimum result(step S164).

The module processor 52 determines whether or not the positioningaccuracy index Δh is equal to or less than a first reference value H1(step S165). The first reference value H1 is a lower limit value ofsufficient positioning accuracy obtained by normal satellitepositioning, and is, for example, 15 (meters). If it is determined thatthe positioning accuracy index Δh is not equal to or less than (that is,larger than) the first reference value H1 (“NO” in step S165), theprocess of the module processor 52 proceeds to step S158.

If is determined that the positioning accuracy index Δh is equal to orless than the first reference value H1 (“YES” in step S165), the moduleprocessor 52 determines whether or not the number of radio signals usedfor the positioning calculation is equal to or more than the referencenumber Ns (lowest setting number) (step S166). As described above, thenumber of radio signals is required to be 4 or more forthree-dimensional positioning calculation, but in order to obtain ahigher positioning accuracy more stably, it is better to have more radiowave signals. Here, “6” is set as the reference number Ns. If it isdetermined that the number of radio signals is equal to or more than thereference number Ns (“YES” in step S166), the process of the moduleprocessor 52 proceeds to step S171.

If it is determined that the number of radio signals used for thepositioning calculation is not equal to or more than (that is, lessthan) the reference number Ns (“NO” in step S166), the module processor52 decides whether or not the current position may be adopted, on thebasis of information on the positioning accuracy in the altitudedirection, here, the presence/absence of a high altitude angle satelliteand the position accuracy index Δz in the altitude direction in thereceived radio wave. The module processor 52 determines whether or not aradio signal from a high altitude angle satellite which sends radiowaves from a predetermined altitude angle (for example, 60 degrees) ormore has been used for positioning calculation (step S167). If it isdetermined to be used (“YES” in step S167), the process of the moduleprocessor 52 proceeds to step S158.

If it is determined that the radio signal from the high altitude anglesatellite is not used for the positioning calculation (“NO” in stepS167), the module processor 52 determines whether or not the accuracyindex Δz of the position in the altitude direction is equal to or morethan an altitude reference value Z1 (step S168). If it is determined tobe equal to or more than the altitude reference value Z1 (“YES” in stepS168), the process of the module processor 52 proceeds to step S158. Ifit is determined not to be equal to or more than (that is, less than)the altitude reference value Z1 (“NO” in step S168), the process of themodule processor 52 moves to step S171.

The processes of the above-described steps S165 and S166 constitute theadoption determiner (adoption determination step in the positioningcontrol method) in the satellite radio wave receiving unit 50 of thepresent embodiment. The adoption determiner (adoption determinationstep) may further include respective processes of steps S158, S161 toS164, S167, and S168.

After proceeding from the respective determination processes of stepsS161, S166, and S168 to the process of step S171, the module processor52 sets the currently stored optimum result as output data. The moduleprocessor 52 stops the operation of the receiver 51 and stops theprocess related to adopting the current position during this one minute(step S171; stop controller, stop control step). Then, the moduleprocessor 52 terminates the intermittent position obtaining process andreturns the process to the positioning control process.

The accuracy condition and the receiving time limit for stopping thereceiving operation need not be fixed and can be set to various valuesdepending on the usage of the positioning result, specifically, the typeand operation mode (high-accuracy mode or power saving mode, etc.) ofthe requesting application software. These values may be changed and seton the basis of the predetermined input operation accepted by theoperation receiver 61.

[Modification]

FIG. 6 is a flowchart illustrating modification of the intermittentposition obtaining process.

The accuracy index value considering both the positional relationship ofthe positioning satellites and the parameters regarding the receptionstate is calculated and used in the above embodiment, however, they maybe separately evaluated. Here, DOP and SNR are separately evaluated.

In the intermittent position obtaining process of this modification, theprocesses of steps S158, S162 to S164, and S168 in the intermittentposition promotion process of the above embodiment are respectivelyreplaced by steps S158 a, S162 a to S164 a, and S168 a, and theprocessing of step S165 is replaced by two processing of step S165 a andstep S165 b. The other processes are the same, and the contents of thesame processes are denoted by the same reference numerals, and adetailed description thereof will be omitted.

If the process proceeds to “NO” in step S161, the module processor 52obtains respective values of the HDOP, the VDOP, and the SNR that havebeen calculated(step S162 a). The module processor 52 determines whetheror not the value of HDOP is equal to or less than a fourth referencevalue H4 corresponding to the second reference value and is equal to orless than the accuracy index minimum value Δhm (here, the minimum valueof HDOP set in step S164 a) (Step S163 a). As in the above case, if theinitial value of the accuracy index minimum value Δhm is the fourthreference value H4, the former comparison is unnecessary. When it isdetermined that either of them is not satisfied (“NO” in step S163 a),the process of the module processor 52 proceeds to step S158 a.

If it is determined that the value of HDOP is equal to or less than thefourth reference value H4 and equal to or less than the accuracy indexminimum value Δhm (“YES” in step S163 a), the module processor 52 setsthe current HDOP value as the accuracy index minimum value Δhm, andseparately stores the corresponding positioning result as the optimumresult (step S164 a). The module processor 52 determines whether or notthe value of HDOP is equal to or less than a third reference value H3(<the fourth reference value H4) corresponding to the first referencevalue H1 (step S165 a). If it is determined that it is not equal to orless than the third reference value H3 (“NO” in step S165 a), theprocess of the module processor 52 proceeds to step S158 a.

If it is determined that the value of HDOP is equal to or less than thethird reference value H3 (“YES” in step S165 a), the module processor 52determines whether or not the value of SNR is equal to or more than areference value L1 (step S165 b). The reference value L1 is a value atwhich sufficient ranging accuracy can be obtained. For example, a valueof about 35 to 40 (dBHz) is set as a value corresponding to the rangingaccuracy of 15 m in FIG. 3. If it is determined that it is not equal toor more than the reference value L1 (“NO” in step S165 b), the processof the module processor 52 proceeds to step S158 a. If it is determinedthat the value is equal to or more than the reference value L1 (“YES” instep S165 b), the process of the module processor 52 proceeds to stepS166.

If the determination process of step S167 proceeds to “NO”, the moduleprocessor 52 determines whether or not the value of the VDOP is equal toor more than an altitude reference value Z2 corresponding to thealtitude reference value Z1 (step S168 a). If it is determined that thealtitude reference value is equal to or more than the altitude referencevalue Z2 (“YES” in step S168 a), the process of the module processor 52proceeds to step S158 a. If it is determined that the value of VDOP isnot equal to or more than the altitude reference value Z2 (“NO” in stepS168 a), the process of the module processor 52 proceeds to step S171.

If the process proceeds to “YES” in step S167, the processing of themodule processor 52 proceeds to step S158 a.

If the process proceeds from each of the steps S157, S163 a, S165 a,S165 b, S167, and S168 a to step S158 a, the module processor 52 updatesand stores the newly calculated positioning result, calculates andstores the respective values of HDOP, VDOP and SNR (step S158 a). Then,the module processor 52 terminates the intermittent position obtainingprocess and returns the process to the positioning control process.

As described above, the satellite radio wave receiving unit 50, which isthe satellite radio wave receiving device of the present embodiment,includes a receiver 51 that performs the operation of receiving radiowaves from the positioning satellite, and a module processor 52 thatcalculates the current position based on the radio wave received by thereceiver 51. The module processor 52 causes the receiver 51 to start thereceiving operation as the activation controller, and calculates thecurrent position as the calculator. The module processor 52 decideswhether or not to adopt the current position based on the number ofpositioning satellites from which the receiver 51 has received the radiowaves and the calculated positioning accuracy of the current position asthe adoption determiner. As the stop controller, the module processor 52stops the receiving operation if the current position is adopted, andcontinues the receiving operation by repeating the calculation of thecurrent position if the current position is not adopted.

In this way, the positioning result is appropriately adopted based onnot only the number of positioning satellites from which radio waves arereceived, but also whether or not a desired positioning accuracy can beobtained in the radio wave receiving state. Therefore, it is possible tomore reliably obtain highly accurate position information whilepreventing the receiving operation from continuing more than necessaryby continuous reception and repeated positioning calculation,considering the case where the receiving state is bad due to thebuilding structure or geographical features in spite of an appropriatearrangement of the positioning satellites, or the case where theincorrectly converged position cannot be properly corrected due to thenumber of positioning satellites is marginal in spite of the goofreceiving state.

Further, the module processor 52 obtains the positioning accuracy on thebasis of the radio wave receiving state from each positioning satellite.Other than the number and position of the positioning satellites fromwhich the radio waves were received, the required positioning accuracyis greatly affected and reduced by the radio wave receiving state.Therefore, by calculating the positioning accuracy also on the basis ofthe radio wave receiving state (in particular, SNR), it is possible toimprove the certainty of the positioning accuracy and to obtain accurateposition information.

Further, the module processor 52 causes the receiver 51 to start thereceiving operation at every predetermined period. That is, since thepositioning result is adopted based on the positioning accuracy asdescribed above in the intermittent positioning, it is possible tocontinually obtain accurate current position information whileappropriately controlling the time for reception operation.

If it is not decided to adopt the current position within the receivingtime limit (30 seconds), which is less than the predetermined period (1minute), the module processor 52 obtains the current position having thehighest positioning accuracy among those calculated within the receivingtime limit (30 seconds) for adoption, and causes the receiver to stopthe receiving operation.

That is, if the current position has been adopted with a certain degreeof accuracy, the receiving operation is terminated suitably rather thancontinued too long, so that an optimum current position is obtained foradoption within the receiving operation time. It is possible toappropriately maintain balance between power consumption and positioningaccuracy.

Further, the module processor 52 adopts the current position if thepositioning accuracy in the horizontal direction satisfies the firstcriterion and if the number of the positioning satellites from which theradio waves are received is the lowest setting number (five) or more.That is, the visible state of low altitude angle positioning satellites,which is likely to affect the horizontal positioning accuracy, tends tochange in a short time. Therefore, by determining whether or not tocontinue the receiving operation and the positioning calculationpreferentially taking the low altitude angle positioning satellites intoconsideration, it is possible to adjust the balance between the powerconsumption and the positioning accuracy more flexibly and appropriatelyand to adopt an accurate current position more stably.

If the positioning accuracy in the horizontal direction satisfies thefirst criterion and the number of positioning satellites from whichradio waves are received is less than the lowest setting number (5), themodule processor 52 decides whether or not to adopt the current positionin consideration of the information on the positioning accuracy in thealtitude direction (the number and the accuracy index Δz of the positionin the altitude direction of high altitude angle satellites). That is,if the number of positioning satellites used for the positioningcalculation is small, even if the positioning accuracy in the horizontaldirection satisfies the criterion, the possibility that the calculationdoes not converge correctly cannot be excluded. Therefore, byconsidering information as to whether or not the component in thealtitude direction of the current position is also accuratelydetermined, it is possible to more accurately determine whether or notthe correct convergence calculation has been performed.

The electronic timepiece 1 of the present embodiment includes the abovesatellite radio wave receiving unit 50 and a timing circuit 47. Withsuch an electronic timepiece, it is possible to adopt the currentposition with higher accuracy while appropriately suppressing the powerconsumption, so that it is possible to miniaturize the necessarybattery. Thus, while suppressing the increase in size and weight of thetimepiece, it is possible to accurately acquire the current position andto perform notification (or to display) to the user.

Further, the positioning control method by the satellite radio wavereceiving unit 50 of the present embodiment includes the followingsteps: an activation control step of causing the receiver 51 to startreceiving operation; a calculation step of calculating a currentposition on the basis of the radio waves received by the receiver 51; anadoption determination step of deciding whether or not to adopt thecurrent position on the basis of the number of positioning satellitesfrom which the receiver 51 has received the radio waves and thecalculated positioning accuracy of the current position; and a stopcontrol step of causing the receiver to stop the receiving operation ifthe current position is adopted, and to continue the receiving operationand to repeat calculation of the current position if the currentposition is not adopted.

With such a positioning control method, the positioning result isappropriately adopted based on not only the number of positioningsatellites from which radio waves are received, but also whether or nota desired positioning accuracy can be obtained in the radio wavereceiving state. Therefore, it is possible to more reliably obtainhighly accurate position information while preventing the receivingoperation from continuing more than necessary by continuous receptionand repeated positioning calculation, considering the case where thereceiving state is bad due to the building structure or geographicalfeatures in spite of an appropriate arrangement of the positioningsatellites, or the case where the incorrectly converged position cannotbe properly corrected due to the number of positioning satellites ismarginal in spite of the goof receiving state.

The above embodiments are examples and various modifications can bemade.

For example, in the case where the positioning is continuouslyperformed, the current position at the next positioning may be estimatedto some extent on the basis of the past movement history. Besides thepositioning calculation, such an estimated position may be obtained andthe difference between the measured position adopted as the positioningresult and the estimated position maybe used as an index of positioningaccuracy.

For example, the moving speed and the moving acceleration are obtainedbased on the amount of change in position obtained from the positioninformation obtained in the most recent multiple times (at least twice).If there is no large acceleration or change thereof, the moving speed ofthe electronic timepiece 1 (the satellite radio wave receiving device)is calculated based on the change in position (and the change in movingspeed as necessary), and the next position is estimated on the basis ofthis moving speed and the previous measured position.

When calculating the positioning accuracy index based on the deviationof the actual measurement from such predicted value, it is not necessaryto use the value of the measured position as it is in consideration ofthe deviation of the previous measured position. Using the previousmeasured position and the previous predicted position, a more likelyplausible previous estimated position may be obtained and used for theestimation of the next position. Any appropriate method may be used forestimating the position, such as a Kalman filter. If the Kalman filteris not used, similar to the covariance matrix of errors in the Kalmanfilter, the estimated position may be obtained by moderately weightingthe positions based on the amount of deviation between the predictedposition and the measured position.

Further, the positioning accuracy index obtained based on such estimatedposition and the above-mentioned positioning accuracy index Δh may beused in combination. The combination method may include, for example,obtaining both of them and simply using the larger one.

In the above embodiment, the positioning accuracy in the horizontaldirection was mainly considered as the positioning accuracy, and thepositioning accuracy in the altitude direction is considered only in aspecific case. However, the three-dimensional directional positioningaccuracy maybe taken into consideration from the beginning.Alternatively, on the contrary, the positioning accuracy in the altitudedirection may not be taken into consideration. Depending on the degreeof significance of position information in the altitude direction, thebranch of “YES” and “NO” in step S167 may be interchanged.

Alternatively, whether or not the positioning result (current position)can be adopted and whether or not the to stop the receiving operationmaybe determined based on the positioning accuracy obtained by variousmethods other than the above.

In the above embodiment, the case of intermittent reception in which thepositioning result is adopted once a minute is described as an example.However, positioning calculation may be repeated until conditions forthe number of positioning satellites and the positioning accuracy aresatisfied, in the case of adopting a single positioning result as well.Further, in the case of intermittent reception, it is not necessary thatthe receiver 51 is periodically activated. The interval of the starttiming of the reception operation by the receiver 51 maybe changedaccording to other conditions, for example, the moving state of thesatellite radio wave receiving device detected by an acceleration sensoror the like. Further, the receiving operation by the receiver 51 may bestarted one (1) minute after the timing when the positioning result wasfinally adopted in the last process.

In the above embodiment, the decision of whether or not to continue thepositioning calculation and the receiving operation is made by themodule processor 52, but it may be made by the host processor 41. Inthis case, information on positioning accuracy and number of satellitesmay be output from the module processor 52 to the host processor 41, sothat the host processor 41 can make the decision based on theinformation. Alternatively, the host processor 41 may calculate thepositioning accuracy.

Although the host processor 41 and the module processor 52 areseparately provided in the above embodiment, an electronic timepiece 1(satellite radio wave receiving apparatus) may have a single processor.In addition, although the module processor 52 as a processor includes aCPU and performs control operation by software in the above embodiment,a dedicated hardware circuit or the like may be provided and a part ofthe process may be performed by the hardware circuit. Alternatively, themodule processor 52 may further include a CPU and RAM for exclusivelyperforming a part of software processing.

In the above description, the programs 631 for positioning control anddisplay settings are stored in a computer-readable medium, including anonvolatile memory such as a flash memory, and/or the ROM 63 such as amask ROM, though not limitative in any way. Any other type ofcomputer-readable recording medium may be used, for example, a portablerecording medium, such as hard disk drive (HDD), CD-ROM, and DVD disk.

It should be understood that the details of the configurations, controlprocedures, and display examples shown in the above embodiment can beappropriately modified without departing from the scope of thedisclosure.

The embodiments described above should not be construed to limit thepresent invention, and the claims and other equivalents thereof areincluded in the scope of the invention.

What is claimed is:
 1. A satellite radio wave receiving devicecomprising: one or more processors configured to: cause a receiver tostart a receiving operation of receiving radio waves from positioningsatellites; perform a current position calculation to calculate acurrent position based on the radio waves received by the receiver;calculate a positioning accuracy of the current position; decide whetheror not to adopt the current position based on a number of positioningsatellites from which the receiver has received radio waves and thepositioning accuracy of the current position; in response to deciding toadopt the current position, cause the receiver to stop the receivingoperation; and in response to deciding to not adopt the currentposition, cause the receiver to continue the receiving operation ofreceiving radio waves from the positioning satellites and repeatperformance of the current position calculation to calculate currentpositions based on the radio waves received during the continuedreceiving operation.
 2. The satellite radio wave receiving deviceaccording to claim 1, wherein the one or more processors are configuredto: determine a receiving state of the radio waves from each of thepositioning satellites; and calculate the positioning accuracy based onthe receiving state of the radio waves from each of the positioningsatellites.
 3. The satellite radio wave receiving device according toclaim 1, wherein the one or more processors are configured to cause thereceiver to start the receiving operation every time a predeterminedperiod elapses.
 4. The satellite radio wave receiving device accordingto claim 2, wherein the one or more processors are configured to causethe receiver to start the receiving operation every time a predeterminedperiod elapses.
 5. The satellite radio wave receiving device accordingto claim 3, wherein the one or more processors are configured to: inresponse to deciding to not adopt the current position, cause thereceiver to continue the receiving operation; repeat calculation of thecurrent position; and calculate positioning accuracies of the currentpositions that are repeatedly calculated; and while causing the receiverto continue the receiving operation of receiving radio waves from thepositioning satellites, determine whether a receiving time limit whichis less than the predetermined period has passed; and in response todetermining that the receiving time limit has passed, adopt one of thecurrent positions having a highest positioning accuracy, and cause thereceiver to stop the receiving operation.
 6. The satellite radio wavereceiving device according to claim 4, wherein the one or moreprocessors are configured to: in response to deciding to not adopt thecurrent position, cause the receiver to continue the receivingoperation; repeat calculation of the current position; and calculatepositioning accuracies of the current positions that are repeatedlycalculated; and while causing the receiver to continue the receivingoperation of receiving radio waves from the positioning satellites,determine whether a receiving time limit which is less than thepredetermined period has passed; and in response to determining that thereceiving time limit has passed, adopt one of the current positionshaving a highest positioning accuracy, and cause the receiver to stopthe receiver operation.
 7. The satellite radio wave receiving deviceaccording to claim 1, wherein the one or more processors are configuredto: in calculating the positioning accuracy of the current position,calculate the positioning accuracy in a horizontal direction; determinewhether the positioning accuracy in the horizontal direction satisfies afirst criterion; and determine whether the number of the positioningsatellites from which radio waves are received is equal to or more thana lowest setting number; and in response to determining that thepositioning accuracy in the horizontal direction satisfies the firstcriterion and the number of the positioning satellites from which radiowaves are received is equal to or more than the lowest setting number,adopt the current position.
 8. The satellite radio wave receiving deviceaccording to claim 2, wherein the one or more processors are configuredto: in calculating the positioning accuracy of the current position,calculate the positioning accuracy in a horizontal direction; determinewhether the positioning accuracy in the horizontal direction satisfies afirst criterion; and determine whether the number of the positioningsatellites from which radio waves are received is equal to or more thana lowest setting number; and in response to determining that thepositioning accuracy in the horizontal direction satisfies the firstcriterion and the number of the positioning satellites from which radiowaves are received is equal to or more than the lowest setting number,adopt the current position.
 9. The satellite radio wave receiving deviceaccording to claim 3, wherein the one or more processors are configuredto: in calculating the positioning accuracy of the current position,calculate the positioning accuracy in a horizontal direction; determinewhether the positioning accuracy in the horizontal direction satisfies afirst criterion; and determine whether the number of the positioningsatellites from which radio waves are received is equal to or more thana lowest setting number; and in response to determining that thepositioning accuracy in the horizontal direction satisfies the firstcriterion and the number of the positioning satellites from which radiowaves are received is equal to or more than the lowest setting number,adopt the current position.
 10. The satellite radio wave receivingdevice according to claim 4, wherein the one or more processors areconfigured to: in calculating the positioning accuracy of the currentposition, calculate the positioning accuracy in a horizontal direction;determine whether the positioning accuracy in the horizontal directionsatisfies a first criterion; and determine whether the number of thepositioning satellites from which radio waves are received is equal toor more than a lowest setting number; and in response to determiningthat the positioning accuracy in the horizontal direction satisfies thefirst criterion and the number of positioning satellites from whichradio waves are received is equal to or more than the lowest settingnumber, adopt the current position.
 11. The satellite radio wavereceiving device according to claim 7, wherein the one or moreprocessors are configured to: in calculating the positioning accuracy ofthe current position, calculate the positioning accuracy in an altitudedirection; and in response to determining that the positioning accuracyin the horizontal direction satisfies the first criterion and the numberof positioning satellites from which radio waves are received is lessthan the lowest setting number, decide whether or not to adopt thecurrent position based on the positioning accuracy in the altitudedirection.
 12. The satellite radio wave receiving device according toclaim 8, wherein the one or more processors are configured to: incalculating the positioning accuracy of the current position, calculatethe positioning accuracy in an altitude direction; and in response todetermining that the positioning accuracy in the horizontal directionsatisfies the first criterion and the number of positioning satellitesfrom which radio waves are received is less than the lowest settingnumber, decide whether or not to adopt the current position based on thepositioning accuracy in the altitude direction.
 13. The satellite radiowave receiving device according to claim 9, wherein the one or moreprocessors are configured to: in calculating the positioning accuracy ofthe current position, calculate the positioning accuracy in an altitudedirection; and in response to determining that the positioning accuracyin the horizontal direction satisfies the first criterion and the numberof positioning satellites from which radio waves are received is lessthan the lowest setting number, decide whether or not to adopt thecurrent position based on the positioning accuracy in the altitudedirection.
 14. The satellite radio wave receiving device according toclaim 10, wherein the one or more processors are configured to: incalculating the positioning accuracy of the current position, calculatethe positioning accuracy in an altitude direction; and in response todetermining that the positioning accuracy in the horizontal directionsatisfies the first criterion and the number of positioning satellitesfrom which radio waves are received is less than the lowest settingnumber, decide whether or not to adopt the current position based on thepositioning accuracy in the altitude direction.
 15. A satellite radiowave receiving device comprising: means for causing a receiver to starta receiving operation of receiving radio waves from positioningsatellites; means for performing a current position calculation tocalculate a current position based on the radio waves received by thereceiver; means for calculating a position accuracy of the currentposition; means for deciding whether or not to adopt the currentposition based on a number of positioning satellites from which thereceiver has received radio waves and the positioning accuracy of thecurrent position; and means for, in response to deciding to adopt thecurrent position, causing the receiver to stop the receiving operation;and means for, in response to deciding to not adopt the currentposition, causing the receiver to continue the receiving operation ofreceiving radio waves from the positioning satellites and repeatingperformance of the current position calculation to calculate currentpositions based on the radio waves received during the continuedreceiving operation.
 16. An electronic timepiece comprising: thesatellite radio wave receiving device according to claim 1; thereceiver; and a clock circuit configured to count a current date andtime.
 17. An electronic timepiece comprising: the satellite radio wavereceiving device according to claim 2; the receiver; and a clock circuitconfigured to count a current date and time.
 18. An electronic timepiececomprising: the satellite radio wave receiving device according to claim3; the receiver; and a clock circuit configured to count a current dateand time.
 19. An electronic timepiece comprising: the satellite radiowave receiving device according to claim 15; the receiver; and a clockcircuit configured to count a current date and time.
 20. A positioningcontrol method performed by a satellite radio wave receiving deviceincluding a receiver, the method comprising: causing the receiver tostart a receiving operation of receiving radio waves from positioningsatellites; performing a current position calculation to calculate acurrent position based on the radio waves received by the receiver;calculating a positioning accuracy of the current position; decidingwhether or not to adopt the current position based on a number ofpositioning satellites from which the receiver has received radio wavesand the positioning accuracy of the current position; in response todeciding to adopt the current position, causing the receiver to stop thereceiver operation; and in response to deciding to not adopt the currentposition, causing the receiver to continue the receiving operation ofreceiving radio waves from the positioning satellites and repeatingcalculation of the current position calculation to calculate currentpositions based on the radio waves received during the continuedreceiving operation.
 21. A non-transitory computer-readable storagemedium storing instructions that cause one or more computers to at leastperform: causing a receiver to start a receiving operation of receivingradio waves from positioning satellites; performing a current positioncalculation to calculate a current position based on the radio wavesreceived by the receiver; calculating a positioning accuracy of thecurrent position; deciding whether or not to adopt the current positionbased on a number of positioning satellites from which the receiver hasreceived radio waves and the positioning accuracy of the currentposition; in response to deciding to adopt the current position, causingthe receiver to stop the receiving operation; and in response todeciding to not adopt the current position, causing the receiver tocontinue the receiving operation of receiving radio waves from thepositioning satellites and repeating performance of the current positioncalculation to calculate current positions based on the radio wavesreceived during the continued receiving operation.